Large-aperture four-piece optical lens

ABSTRACT

A large-aperture four-piece optical lens includes a first lens with positive focal power, a second lens with negative focal power, a third lens with positive focal power and a fourth lens with positive focal power which are sequentially arranged. A back of the fourth lens is provided with an image surface, an aperture diaphragm is arranged at a front end of the first lens or between the second lens and the third lens, and a vignetting diaphragm is arranged on an S7 surface of the fourth lens. An equivalent focal length of the fourth lens is greater than that of the third lens, and the equivalent focal length of the fourth lens is greater than that of the first lens. Each lens has a low sensitivity to an axial tolerance and a low assembly difficulty, and an energy utilization rate can be improved by increasing a numerical aperture.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims priority to and the benefit of Chinese PatentApplication No. CN202110064542.5 filed in China on Jan. 18, 2021. Thedisclosure of the above application is incorporated herein in itsentirety by reference.

TECHNICAL FIELD

The present invention relates to an optical lens, and more particularly,to a large-aperture four-piece optical lens.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

In traditional technologies, a headlight lens based on a projectionprinciple is composed of a light source, a light energy collectingmember, a cut-off line structure and a convex lens.

A light digital projection technology is used in a newly developed pixelheadlight which is also known as a matrix headlight, so that theheadlight not only has a lighting function, but also can projectpatterns on the ground, such as weather conditions, road navigation, orother symbols for identification by people outside a vehicle. An opticalsystem of the pixel headlight mainly comprises an illuminable pixel(such as mini LED, micro LED, LCD screen, LCOS or lightened DMD digitalmicrolens) and a projection optical lens. In order to make theprojection pattern clearly visible, the lens needs to have a goodoptical performance: chromatic aberration, field curvature, astigmatismand other optical aberrations are eliminated.

For the optical lens in the prior art, a plurality of positive andnegative lenses need to be properly combined for joint use, so as toeliminate aberration. A specific number of the optical lenses used isrelated to parameters, performance indexes, and used optical materialsand optical processes of the optical lenses, and a slightly complicatedoptical lens may be provided with more than 10 lenses. The optical lenscurrently used in a mobile phone is provided with more than 6 lenses,with a high cost.

In traditional technologies, the imaging quality of a Cook's three-piecelens is difficult to meet requirements. FIG. 1 shows a classicfour-piece three-set Tessar lens, which is evolved from the Cook'sthree-piece lens, that is, the last set of single convex lenses is adouble-cemented lens. The Tessar lens has sharp imaging and goodcorrection for various aberrations, but a numerical aperture of originaldesign is small, and is generally only about 0.125 and less than 0.2,which means that a utilization rate of light energy is extremely low,and the lenses need to be adjusted very accurately in assembly and use,with small tolerance and high use requirements. A four-piece doubleGauss lens also has the above problems.

The headlight has both lighting and imaging functions. On one hand, ahigher energy utilization rate and a higher brightness are needed, andon the other hand, there are certain image quality requirements for aprojected image, especially low chromatic aberration. In addition, dueto a particularity of automobile application, the optical lens needs tohave a higher thermal reliability, a better vibration reliability and alower mass, and in order to further improve the market competitiveness,a lower cost is needed at the same time.

The optical lens in the prior art cannot meet the performancerequirements of a high energy utilization rate, a high imaging quality,a simple and stable structure and a low cost at the same time.

SUMMARY

Aiming at the problems in the prior art above, the present inventionprovides a large-aperture four-piece optical lens, which has a highenergy utilization rate, a high imaging quality, a simple and stablestructure and low manufacturing and using cost.

The large-aperture four-piece optical lens provided by the presentinvention comprises a first lens with positive focal power, a secondlens with negative focal power, a third lens with positive focal powerand a fourth lens with positive focal power which are sequentiallyarranged, wherein two surfaces of the first lens are an S1 surface andan S2 surface respectively, two surfaces of the second lens are an S3surface and an S4 surface respectively, two surfaces of the third lensare an S5 surface and an S6 surface respectively, two surfaces of thefourth lens are an S7 surface and an S8 surface respectively, the S1surface, the S2 surface, the S3 surface, the S4 surface, the S5 surface,the S6 surface, the S7 surface and the S8 surface are sequentiallyarranged, a side of the S8 surface far away from the S7 surface isprovided with an S9 surface, an aperture diaphragm is arranged on a sideof the Si surface or between the S2 surface and the S3 surface, avignetting diaphragm is arranged on the S7 surface, the S1 surface, theS2 surface, the S5 surface, the S6 surface and the S7 surface are allconvex surfaces, and the S4 surface is a concave surface;

a distance between the aperture diaphragm and an object focal point ofthe lens is |ST-F_(obj)|, and an equivalent focal length of the lens isf₀, |ST−F_(obj)|<0.7f₀;

an aperture d of the S1 surface to the S8 surface satisfies thefollowing relationship: d_(i)>0.9d_(j), i<j, i is an integer rangingfrom 1 to 7, and j is an integer ranging from 2 to 8;

a radius of curvature of the S3 surface is r₃, a radius of curvature ofthe S4 surface is r₄, |r₄|<|r₃|, a radius of curvature of the S7 surfaceis r₇, a radius of curvature of the S8 surface is r₈, |r₇|<|r₈|, anequivalent focal length of the fourth lens is greater than that of thethird lens, and the equivalent focal length of the fourth lens isgreater than that of the first lens; and

a distance between centers of the S6 surface and the S7 surface is G₆₇,and a distance between centers of the S2 surface and the S3 surface isG₂₃, G₆₇<G₂₃.

Preferably, a rear intercept of the lens is greater than 2 mm.

Preferably, the S8 surface is a flat surface or a concave surface.

Preferably, the S1 surface, the S2 surface, the S3 surface, the S4surface, the S5 surface, the S6 surface, the S7 surface and the S8surface are spherical surfaces or aspherical surfaces.

Preferably, the first lens, the second lens, the third lens and thefourth lens are single lenses or cemented lenses.

Preferably, the first lens, the second lens, the third lens and thefourth lens are glass lenses or plastic lenses.

Further, an Abbe number of the first lens is Vd₁, an Abbe number of thesecond lens is Vd₂, an Abbe number of the third lens is Vd₃, and an Abbenumber of the fourth lens is Vd₄, Vd₁−Vd₂>25, Vd₃−Vd₂>25, Vd₄−Vd₂>25.

The present invention has the beneficial effects that: the presentinvention discloses the large-aperture four-piece optical lens, onlyfour lenses are used in the lens, with a low manufacturing cost, asimple and stable overall structure, a good anti-vibration performanceand a low lens mass, and the lenses have a low sensitivity to axialtolerance in assembly, with a large tolerance rate, a low assemblydifficulty and a low assembly cost; and an energy utilization rate canbe improved by increasing the numerical aperture, which can effectivelyimprove a brightness of light distribution, and when applied to theprojection imaging system, the optical lens has a good chromaticdispersion performance and a good image resolution, which means that theoptical lens has a high imaging quality.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in detail below in conjunctionwith embodiments and accompanying drawings, in which:

FIG. 1 is a schematic structural diagram of a lens system of a Tessarlens.

FIG. 2 is a schematic structural diagram of Embodiment 1 of the presentinvention.

FIG. 3 is a graph of an astigmatism and field curvature curve and adistortion curve in Embodiment 1 of the present invention.

FIG. 4 is a graph of an on-axis chromatic aberration curve in Embodiment1 of the present invention.

FIG. 5 is a graph of a MTF curve in Embodiment 1 of the presentinvention.

FIG. 6 is a schematic structural diagram of Embodiment 2 of the presentinvention.

FIG. 7 is a graph of an astigmatism and field curvature curve and adistortion curve in Embodiment 2 of the present invention.

FIG. 8 is a graph of an on-axis chromatic aberration curve in Embodiment2 of the present invention.

FIG. 9 is a graph of a MTF curve in Embodiment 2 of the presentinvention.

Reference numerals: 10 refers to first lens, 11 refers to S1 surface, 12refers to S2 surface, 20 refers to second lens, 21 refers to S3 surface,22 refers to S4 surface, 30 refers to third lens, 31 refers to S5surface, 32 refers to S6 surface, 40 refers to fourth lens, 41 refers toS7 surface, 42 refers to S8 surface, 50 refers to S9 surface, 60 refersto aperture diaphragm, and 70 refers to vignetting diaphragm.

DETAILED DESCRIPTION

In order to further understand the features, the technical means, andthe achieved specific objectives and functions of the present invention,the present invention is further described in detail hereinafter withreference to the accompanying drawings and the specific embodiments.

With reference to FIG. 1 to FIG. 9,

a basic embodiment of the present invention discloses a large-aperturefour-piece optical lens, which comprises a first lens 10 with positivefocal power, a second lens 20 with negative focal power, a third lens 30with positive focal power and a fourth lens 40 with positive focal powerwhich are sequentially arranged along a light incident direction. Twosurfaces of the first lens 10 are an S1 surface 11 and an S2 surface 12respectively, two surfaces of the second lens 20 are an S3 surface 21and an S4 surface 22 respectively, two surfaces of the third lens 30 arean S5 surface 31 and an S6 surface 32 respectively, and two surfaces ofthe fourth lens 40 are an S7 surface 41 and an S8 surface 42respectively. The S1 surface 11, the S2 surface 12, the S3 surface 21,the S4 surface 22, the S5 surface 31, the S6 surface 32, the S7 surface41 and the S8 surface 42 are sequentially arranged along a lightincident direction. A side of the S8 surface 42 far away from the S7surface 41 is provided with an S9 surface 50, and the S9 surface 50 isan image surface, which means that the S9 surface 50 is located at animage focal point of a whole optical lens. An aperture diaphragm 60 isarranged on a side of the S1 surface 11 or between the S2 surface 12 andthe S3 surface 21. Ideally, the aperture diaphragm 60 is located on aside of the S1 surface 11 far away from the S2 surface 12. When appliedto a vehicle headlight lens, considering a modeling design requirement,the aperture diaphragm 60 may be arranged between the S2 surface 12 andthe S3 surface 21, so that a structural body of the aperture diaphragm60 can be hidden inside the lens, and the structural body of theaperture diaphragm 60 cannot be observed outside the vehicle headlightlens. A vignetting diaphragm 70 is arranged on the S7 surface 41, andthe vignetting diaphragm 70 is generally a lens mount. The S1 surface11, the S2 surface 12, the S5 surface 31, the S6 surface 32 and the S7surface 41 are all convex surfaces, and the S4 surface 22 is a concavesurface.

A distance between the aperture diaphragm 60 and an object focal pointof the whole optical lens is |ST-F_(obj)|, ST represents a distancebetween the aperture diaphragm 60 and a center of the whole opticallens, and F_(obj) represents a distance between the object focal pointof the whole optical lens and the center of the whole optical lens. Anequivalent focal length of the whole optical lens is f₀, and inpractical application, the object focal point of the whole optical lensmay be inside the first lens 10, so that the aperture diaphragm 60 isarranged near the object focal point of the whole optical lens, whichmeans that the following formula: |ST−F_(obj)|<0.7f₀ is satisfied.

Apertures d₁˜d₈ of the S1 surface 11 to the S8 surface 42 satisfy thefollowing relationship: d_(i)>0.9d_(j), i<j, i is an integer rangingfrom 1 to 7, j is an integer ranging from 2 to 8, and d is an apertureof a corresponding optical surface. Along a light incident direction,the apertures of the S1 surface 11 to the S8 surface 42 are changedbasically conforming to a trend of gradual decrease.

A radius of curvature of the S3 surface 21 is r₃, a radius of curvatureof the S₄ surface 22 is r₄, |r₄|<|r₃|, and a radius of curvature of theS7 surface 41 is r₇, a radius of curvature of the S8 surface 42 is r₈,|r₇|<|r₈|. An equivalent focal length of the fourth lens 40 is greaterthan that of the third lens 30, that is, f₄>f₃, and the equivalent focallength of the fourth lens 40 is greater than that of the first lens 10,that is, f₄>f₁.

A distance between centers of the S6 surface 32 and the S7 surface 41 isG₆₇, and a distance between centers of the S2 surface 12 and the S3surface 21 is G₂₃, G₆₇<G₂₃.

In operation, a ray sequentially reaches the S1 surface 11, the S2surface 12, the S3 surface 21, the S4 surface 22, the S5 surface 31, theS6 surface 32, the S7 surface 41, the S8 surface 42 and the S9 surface50. The optical lens of the present invention can significantly improvea chromatic dispersion performance of a vehicle headlight, and reduce asensitivity of the lens to axial tolerance in assembly, with a highassembly tolerance rate and a low assembly difficulty.

For a Tessar lens based on a classic Cook's three-piece variant, asshown in FIG. 1, the aperture diaphragm is generally arranged at amiddle lens, which can reduce or correct common aberration, such asfield curvature, astigmatism and chromatic aberration, throughstructural symmetry. However, this structure, on one hand, may lead to asmall numerical aperture for describing an overall light energyutilization rate; and on the other hand, may also lead to a very largechief ray angle CRA of a chief ray of a large field of view on an imagesurface. An illumination intensity of a general light source satisfies aLambert's cosine law, and the illumination intensity is maximum at a0-degree position, decays to 0.5 at a 60-degree position, and is 0 at a90-degree position. Due to a large chief ray angle CRA, it is indicatedthat energy obtained by the lens system is lower for a solid angle ofthe same size.

According to the present invention, the aperture diaphragm 60 isarranged at the object focal point of the optical lens, thus forming animage space telecentric lens, so that the chief rays of the fields ofview are parallel, that is, the chief ray angles CRA of the chief raysof the fields of view on the image surface which is namely the S9surface 50 are all 0 degree, which means that the energy utilizationrate of the present invention is higher for the solid angle of the samesize. In practical application, the aperture diaphragm 60 is arrangednear the object focal point of the optical lens, and the chief rayangles of the chief rays of the fields of view on the image surfacewhich is namely the S9 surface 50 are all less than 20 degrees, with ahigh energy utilization rate.

In the embodiment, a rear intercept of the lens is greater than 2 mm,which means that a distance between the S8 surface 42 and the S9 surface50 is greater than 2 mm. Since the light source may generate a certainamount of heat in use, the four-piece optical lens provided withsufficient rear intercept can effectively avoid deformation of partscaused by heating.

In the embodiment, the S8 surface 42 is a flat surface or a concavesurface. In the embodiment, the S1 surface 11, the S2 surface 12, the S3surface 21, the S4 surface 22, the S5 surface 31, the S6 surface 32, theS7 surface 41 and the S8 surface 42 are spherical surfaces or asphericalsurfaces, which means that the S1 surface 11 to the S8 surface 42 mayall be spherical surfaces, or the S1 surface 11 to the S8 surface 42 mayall be aspherical surfaces, or the S1 surface 11 to the S8 surface 42comprise spherical surfaces and aspherical surfaces. The asphericalsurface is a rationally designed surface type.

In the embodiment, the first lens 10, the second lens 20, the third lens30 and the fourth lens 40 are single lenses or cemented lenses, whichmeans that the first lens 10, the second lens 20, the third lens 30 andthe fourth lens 40 may all be single lenses, or the first lens 10, thesecond lens 20, the third lens 30 and the fourth lens 40 may all becemented lenses, or the first lens 10, the second lens 20, the thirdlens 30 and the fourth lens 40 comprise single lenses and cementedlenses. The cemented lens, also known as an achromatic lens, is formedby cementing two single lenses, and a multi-color imaging performance ofthe cemented lens is much better than that of the single lens.

In the embodiment, the first lens 10, the second lens 20, the third lens30 and the fourth lens 40 are glass lenses or plastic lenses, whichmeans that the first lens 10, the second lens 20, the third lens 30 andthe fourth lens 40 may all be glass lenses, or the first lens 10, thesecond lens 20, the third lens 30 and the fourth lens 40 may all beplastic lenses, or the first lens 10, the second lens 20, the third lens30 and the fourth lens 40 comprise glass lenses and plastic lenses.

In the embodiment, an Abbe number of the first lens 10 is Vd₁, an Abbenumber of the second lens 20 is Vd₂, an Abbe number of the third lens 30is Vd₃, and an Abbe number of the fourth lens 40 is Vd₄, Vd₁−Vd₂>25,Vd₃−Vd₂>25, Vd₄−Vd₂>25.

In Embodiment 1, a structure of an optical lens is shown in FIG. 2, andthe optical lens is arranged according to Table 1, Table 2, Table 3 andTable 4 below.

TABLE 1 Parameters of surfaces in Embodiment 1 Serial No. Type of Radiusof curvature Thickness Refractive Abbe number Aperture of surfacesurface r (mm) (mm) index n Vd d Object Spherical Infinity 25,000surface surface Aperture Spherical Infinity 0.00 41.88 diaphragm surfaceS1 Aspherical 46.83 15.42 1.492 57.98 41.89 surface S2 Aspherical −10.404.50 41.08 surface S3 Aspherical 20.42 2.43 1.584 27.86 30.35 surface S4Aspherical 4.62 6.56 25.75 surface S5 Spherical 20.99 13.80 1.487 70.4226.50 surface S6 Spherical −30.17 0.09 25.59 surface S7 Spherical 17.9611.24 1.755 52.30 20.65 surface S8 Spherical 54.09 4.31 14.42 surface S9Spherical Infinity 0.00 10.00 surface

An expression of the aspherical surface is as follows:

$z = {\frac{cr^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}r^{2}}}} + {Ar^{4}} + {Br^{6}} + {Cr^{8}} + {Dr^{10}} + {Er^{12}} + {Fr^{14}} + {Gr^{16}} + {Hr^{18}} + {Jr}^{20}}$

wherein z is a vector height of an r position on the aspherical surface,c is a paraxial curvature of the aspherical surface, c=1/r, r is aradius of curvature, k is a conic coefficient, and A to J arehigher-order coefficients.

TABLE 2 Parameters of aspherical surfaces in Embodiment 1 S1 S2 S3 S4Conic coefficient k 0 −4.932 −8.84E−01 −1.77E+00 A −1.90E−05   1.10E−05−1.07E−04   5.28E−06 B   9.32E−08 −4.95E−08   3.52E−07   1.25E−07 C−3.69E−10   6.47E−11 −6.71E−10 −6.40E−10 D   6.38E−13   4.00E−16  3.73E−13   8.26E−13 E −3.68E−16 0 0 0 Other higher-order coefficientsare all 0

TABLE 3 Design parameters of optical lenses in Embodiment 1 Equivalentfocal f1₁ f1₂ f1₃ f1₄ Rear Numerical 1/2 FOV Parameter length f₀ (mm)(mm) (mm) (mm) (mm) intercept f/EPD aperture NA (°) Value 28.3 19.00−10.81 27.85 31.41 4.30 0.67 0.74 10.0

TABLE 4 Constrained relationships in Embodiment 1 Constrainedrelationship Result |ST − F_(obj)| < 0.7f₀ |ST − F_(obj)| = 12.81 mm, sothat the condition is satisfied Aperture d_(i) > 0.9d_(j) It can be seenfrom Table 1 that the condition is satisfied The S7 surface is providedA vignetting coefficient of ½ FOV is 0.45 with the vignetting diaphragm|r₄| < |r₃| It can be seen from Table 1 that the condition is satisfiedr₄ < 0 It can be seen from Table 1 that the condition is satisfied f₄ >f₃ It can be seen from Table 3 that the condition is satisfied f₄ > f₁It can be seen from Table 3 that the condition is satisfied |r₇| < |r₈|It can be seen from Table 1 that the condition is satisfied G₆₇ < G₂₃ Itcan be seen from Table 1 that the condition is satisfied The rearintercept is greater It can be seen from Table 3 that the rear interceptis 4.3 than 2 mm mm, and the condition is satisfied

To sum up, it can be seen that the numerical aperture in Embodiment 1reaches 0.74, which is much greater than 0.125 of the Tessar lens, sothat the energy utilization rate is significantly improved. Anastigmatism and field curvature curve and a distortion curve inEmbodiment 1 are shown in FIG. 3, an on-axis chromatic aberration curveis shown in FIG. 4, and a MTF (Modulation Transfer Function) curve isshown in FIG. 5. It can be seen that the optical lens has a good imagingquality when applied to a projection imaging system.

In Embodiment 2, a structure of an optical lens is shown in FIG. 6, andthe optical lens is arranged according to Table 5, Table 6, Table 7 andTable 8 below.

TABLE 5 Parameters of surfaces in Embodiment 2 Serial No. of Type ofRadius of Thickness Refractive Abbe surface surface curvature r (mm)(mm) index n number Vd Aperture d Object Spherical Infinity 25000surface surface S1 Aspherical 42.622 8.510 1.492 57.98 28.93 surface S2Aspherical −12.870 7.441 28.16 (aperture surface diaphragm) S3Aspherical −115.860 2.390 1.584 27.86 20.16 surface S4 Aspherical 4.6412.626 18.30 surface S5 Aspherical 7.185 9.354 1.586 60.60 19.07 surfaceS6 Aspherical −22.594 1.789 17.65 surface S7 Spherical 11.890 5.6131.755 52.30 12.47 surface S8 Spherical 20.294 3.115  9.74 surface S9Spherical Infinity 0.00  7.99 surface

An expression of the aspherical surface is as follows:

$z = {\frac{cr^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}r^{2}}}} + {Ar^{4}} + {Br^{6}} + {Cr^{8}} + {Dr^{10}} + {Er^{12}} + {Fr^{14}} + {Gr^{16}} + {Hr^{18}} + {Jr}^{20}}$

wherein z is a vector height of an r position on the aspherical surface,c is a paraxial curvature of the aspherical surface, c=1/r, r is aradius of curvature, k is a conic coefficient, and A to J arehigher-order coefficients.

TABLE 6 Parameters of aspherical surfaces in Embodiment 2 S1 S2 S3 S4 S5S6 Conic −7.17110872 −5.588   9.36E+00 −2.54E+00 −2.88 −25.40coefficient k A   3.56E−06   2.36E−06   7.44E−05   8.32E−05   6.35E−05−2.22E−04 B −8.65E−08 −2.25E−08 −1.42E−06   5.47E−07   1.04E−06  3.70E−06 C   2.83E−10 −8.74E−11   1.14E−08 −4.13E−08 −8.28E−09−1.79E−08 D −6.66E−13   2.12E−13 −1.02E−10   2.43E−10     0E+00  0.00E+00 E   0.00E+00     0E+00   4.73E−13     0E+00     0E+00    0E+00 Other higher-order coefficients are all 0

TABLE 7 Design parameters of optical lenses in Embodiment 2 Equivalentfocal f1₁ f1₂ f1₃ f1₄ Rear Numerical 1/2 FOV Parameter length f₀ (mm)(mm) (mm) (mm) (mm) intercept f/EPD aperture NA (°) Value 18.89 21.10−7.51 10.49 29.41 3.12 0.67 0.75 12.0

TABLE 8 Constrained relationships in Embodiment 2 Constrainedrelationship Result |ST − F_(obj)| < 0.7f₀ |ST − F_(obj)| = 6.62 mm, sothat the condition is satisfied Aperture d_(i) > 0.9d_(j) It can be seenfrom Table 5 that the condition is satisfied The S7 surface is providedA vignetting coefficient of ½ FOV is 0.72 with the vignetting diaphragm|r₄| < |r₃| It can be seen from Table 5 that the condition is satisfiedr₄ < 0 It can be seen from Table 5 that the condition is satisfied f₄ >f₃ It can be seen from Table 7 that the condition is satisfied f₄ > f₁It can be seen from Table 7 that the condition is satisfied |r₇| < |r₈|It can be seen from Table 5 that the condition is satisfied G₆₇ < G₂₃ Itcan be seen from Table 5 that the condition is satisfied The rearintercept is greater It can be seen from Table 7 that the rear interceptis 3.12 than 2 mm mm, and the condition is satisfied

To sum up, it can be seen that the numerical aperture in Embodiment 2reaches 0.75, which is much greater than 0.125 of the Tessar lens, sothat the energy utilization rate is significantly improved. Anastigmatism and field curvature curve and a distortion curve inEmbodiment 2 are shown in FIG. 7, an on-axis chromatic aberration curveis shown in FIG. 8, and a MTF (Modulation Transfer Function) curve isshown in FIG. 9. It can be seen that the optical lens has a good imagingquality when applied to a projection imaging system.

The above embodiments only express some implementation modes of thepresent invention, and the descriptions thereof are specific anddetailed, but cannot be understood as limiting the scope of the patentof the present invention. It shall be pointed out that those of ordinaryskills in the art may further make several modifications andimprovements without departing from the concept of the presentinvention, and these modifications and improvements all fall within thescope of protection of the present invention. Therefore, the scope ofprotection of the patent of the present invention shall be subject tothe appended claims.

What is claimed is:
 1. A large-aperture four-piece optical lens,comprising a first lens (10) with positive focal power, a second lens(20) with negative focal power, a third lens (30) with positive focalpower and a fourth lens (40) with positive focal power which aresequentially arranged, wherein two surfaces of the first lens (10) arean S1 surface (11) and an S2 surface (12) respectively, two surfaces ofthe second lens (20) are an S3 surface (21) and an S4 surface (22)respectively, two surfaces of the third lens (30) are an S5 surface (31)and an S6 surface (32) respectively, two surfaces of the fourth lens(40) are an S7 surface (41) and an S8 surface (42) respectively, the Sisurface (11), the S2 surface (12), the S3 surface (21), the S4 surface(22), the S5 surface (31), the S6 surface (32), the S7 surface (41) andthe S8 surface (42) are sequentially arranged, a side of the S8 surface(42) far away from the S7 surface (41) is provided with an S9 surface(50), an aperture diaphragm (60) is arranged on a side of the S1 surface(11) or between the S2 surface (12) and the S3 surface (21), avignetting diaphragm (70) is arranged on the S7 surface (41), the S1surface (11), the S2 surface (12), the S5 surface (31), the S6 surface(32) and the S7 surface (41) are all convex surfaces, and the S4 surface(22) is a concave surface; a distance between the aperture diaphragm(60) and an object focal point of the lens is |ST-F_(obj)|, and anequivalent focal length of the lens is f₀, |ST-F_(obj)|<0.7f₀; anaperture d of the S1 surface (11) to the S8 surface (42) satisfies thefollowing relationship: d_(i)>0.9d_(j), i<j, i is an integer rangingfrom 1 to 7, and j is an integer ranging from 2 to 8; a radius ofcurvature of the S3 surface (21) is r₃, a radius of curvature of the S4surface (22) is r₄, |r₄|<|r₃|, a radius of curvature of the S7 surface(41) is r₇, a radius of curvature of the S8 surface (42) is r₈,|r₇|<|r₈|, an equivalent focal length of the fourth lens (40) is greaterthan that of the third lens (30), and the equivalent focal length of thefourth lens (40) is greater than that of the first lens (10); and adistance between centers of the S6 surface (32) and the S7 surface (41)is G₆₇, and a distance between centers of the S2 surface (12) and the S3surface (21) is G₂₃, G₆₇<G₂₃.
 2. The large-aperture four-piece opticallens according to claim 1, wherein a rear intercept of the lens isgreater than 2 mm.
 3. The large-aperture four-piece optical lensaccording to claim 1, wherein the S8 surface (42) is a flat surface or aconcave surface.
 4. The large-aperture four-piece optical lens accordingto claim 1, wherein the S1 surface (11), the S2 surface (12), the S3surface (21), the S4 surface (22), the S5 surface (31), the S6 surface(32), the S7 surface (41) and the S8 surface (42) are spherical surfacesor aspherical surfaces.
 5. The large-aperture four-piece optical lensaccording to claim 1, wherein the first lens (10), the second lens (20),the third lens (30) and the fourth lens (40) are single lenses orcemented lenses.
 6. The large-aperture four-piece optical lens accordingto claim 1, wherein the first lens (10), the second lens (20), the thirdlens (30) and the fourth lens (40) are glass lenses or plastic lenses.7. The large-aperture four-piece optical lens according to claim 1,wherein an Abbe number of the first lens (10) is Vd₁, an Abbe number ofthe second lens (20) is Vd₂, an Abbe number of the third lens (30) isVd₃, and an Abbe number of the fourth lens (40) is Vd₄, Vd₁−Vd₂>25,Vd₃−Vd₂>25, Vd₄−Vd₂>25.